Bolt for a firearm



Sept 13, 1955 c. H. TAYLOR 2,717,535

BOLT FOR A FIREARM Filed Nov. 19, 1951 EEE-il H T-myl 1:1 :D

United States Patent O BOLT FR A FIREARM Cecil' H. Taylor, New Milford, Conn., assignor to the United States of America as represented by the Secretary of theA Army Application November 19,1951, Serial No. 257,011

6 Claims. (Cl. 89-184) This invention relates to an improvement in the bolt mechanism of a machine gun.

The invention herein described represents an improvement over mechanisms now employed in present-day machine gunsand more particularly to the cal. .60 Tl7E3 machine gun.

One object of this invention is to provide a breech bolt mechanism whereby the rebound of the bolt, in the battery position, is materially diminished.

Another object of this invention is to dampen the counter-recoil impact of the bolt nose-cams against the bolt head rollers of a bolt mechanism, thereby eliminating possible battering and also the longitudinal splitting of the bolt.

A further object of this invention is to provide friction braking means for substantially diminishing the impact of a bolt body on a bolt head during movement into the battery position.

Still another object of this invention is to provide a bolt mechanism having the nose-cams of a bolt separate parts thereof permitting replacement of same without discarding the entire bolt.

A specific object of the present invention lies in the provision of a combined buffer and friction brake means intermediate a bolt head and a bolt body which is also adapted to substantially reduce or eliminate the bounce imparted to the bolt body upon impact wtih the rear end of the bolt head.

Additional objects, advantages, and features of this invention reside in the construction, arrangement, and combination of parts involved in the embodiment of the invention, as will appear or be understood from the following description and accompanying drawings in which:

Fig. l is a fragmentary longitudinal view partially in section showing the bolt mechanism in the unlocked battery position;

Fig. 2 is a view similar to Fig. l with the bolt mechanism in the locked battery position prior to the nal inertia movement of the nose cams;

Fig. 3 is an exploded view of the bolt mechanism;

Fig. 4 is the top perspective View of the mechanism during relative movement between the bolt body and the bolt head; and

Fig. 5 is a perspective View of the inertia block.

Referring to the drawing, reference numerals 12 and 14 designate the breech housing or receiver and barrel respectively of a caliber .60 machine gun. Numeral 16 designates generally the cover for the breech housing 12 which is pivotally secured to the breech housing at 18. On the rear end of barrel 14 there is provided suitable interlocking locks 20 which lock the barrel 14 in fixed relationship to a breech ring 22. The receiver 12 is constructed to guide a bolt assembly generally designated by 24 when such assembly is reciprocating between a recoil and battery position.

Bolt assembly 24 comprises a bolt 26 and a bolt head 28 mounted therein for partial rotation relative to the bolt 26. Bolt head 28 is provided with a shank 30 which Z,7l7,5f35 Patented Sept. 13, 1955 ice telescopes` intol an unlocking cam 32 carried within a bore 34 provided. in the forward portion of bolt 26. Unlocking carn 32 is` provided with oppositely disposed' cam slots 36 for a purpose to be described later.

A tiring pin` 38 is carried by the bolt 26 and projectsv througha conventional aperture (not shown) in bolt head 28. Bolt head 28 is providedV with interrupted ring segments 42 which arel adapted to interlock with complementary interrupted ring segments 44 provided within thev breech ring 22T upon approximately a seventh of a turn. of the bolt head 28. Rearwardly of and aligned withring segments 42 of bolt head 28 there is provided a pair of. studs 58- oppositely disposed and arranged for mounting a pair of rollers 46 to cooperate with cam surfaces 48 located on the rear of breech ring 22. On the rear end ofshank 30 are provided oppositely disposed cam segments 60 toV cooperate with cam slots 36 in unlocking cam 32 for rotating bolt head 28 out of locked position when the firearm is manually charged.

On each side of bolt 26 a slot 50 is located in the forward end thereofto receive an inertia block or cam 52 slidably mounted therein. Cam 52 comprises a front cam nose portion S4 for cooperation with rollers 4'6 and av buffer portion 56 disposed rearwardly thereof. Slots 50 are horizontally disposed and terminate in a transverse recess 62 that intersects bore 34 of bolt 26. Buffer portion 56 is L.shaped in formation and the foot portion 64 of such formationV is receivable in recess 62 for longitudinal movement therein. An arcuate surface 82 is provided on the foot portion 64 and when such portion is assembled in recess 62, the arcuate surfaces 82 of each cam 52 face each other thereby forming a bearing support for bolt headshank 30. To movably retain cam 52 in slot 50,. a pin 66 and roller 68 are vertically mounted in bolt 26 throughl each slot 50 and extend through an elongated slot 70 of cam S2. Cam 52 is biased forwardly by a spring 72 that is seatedV in a recess 74 of cam 52. Biasing of cam. 52 is permitted by the elongation of slot '10.

Upon release of' bolt assembly 24 by a sear (not shown) from the recoil position, such assembly moves forward with each nose cam 52 projecting forwardly of "bolt 26 to. the extent permittedv by the engagement of the rear endwal-l of elongated slot 70 with lixed roller pin 68. At the sameK time, bolt head 28 projects forwardly from bolt. 26 to the extent permitted by the engagement of. cam segments on shank 3l) with a suitable shoulder H84. provided in the rear face of each nose cam 52. In

these positions of nose cams 52 and bolt head 28, only the extreme forward ends of nose cam portions 54 are in contact with bolt head rollers 46 at the moment such rollers. strike the cam surfaces 48 on the breech ring 22 so as to initiate rotation of the bolt head 28. Accordingly, rollers 4.6 of the rotating bolt head 28 act against nose cam portions 54 to drive nose cams 52 rearwardly in slots 50 of counter-recoiling bolt 26. The pressure of bolt head rollers 46 on helical nose cam portions 54 produces a lateral component of force which simultaneous spreads nose cams 52 apart into frictional contact with the sidewalls of receiver 12. The consequent friction-braking effect of nose cams 52 serves to diminish the impact produced when said cams bottom in slots 50 to become an integral part of bolt 26 as shown in Fig. 2. This braking action of nose cams 52 continues during the subsequent peak camming pressure between cam portions 54 and bolt head rollers 46 and thereby substantially diminishes the counter-recoiling energy of bolt 26. Rotation of the bolt head causes the interrupted position during the tiring of a cartridge 76 in accordance with well-known practice. When bolt head 28 has been rotated to a fully locked battery position, the rear end thereof is struck by the forwardly moving bolt 26. Although the friction-damping effect of nose cams 52 has absorbed much of the counter-recoiling energy of bolt 26, the remaining energy thereof is often suicient to cause such rebound thereof as to partially rotate bolt head 28 out of locked battery position prior to the complete ignition of chambered cartridge 76. However, this rebounding tendency of bolt 26 is counteracted by the forward movement imparted to nose cams 52 as a result of the inertia effect thereon when the counter-recoil movement of bolt 26 is halted through impact upon the rear end of bolt head 28. At such time, the contact point between bolt head rollers 46 and the cam surfaces of nose portions 54 has moved substantially beyond the area of the peak camming pressure therebetween and consequently the frictional engagement of nose cams 52 with receiver 12 is insufficient to prevent the inertia movement imparted thereto upon cessation of the counterrecoil of bolt 26.

After bolt assembly 24 has been properly locked in the firing position, the tiring pin 38 is carried forward relative to the bolt head 28 into the firing position in a conventional manner. Firing of the cartridge 76 causes recoil of the barrel 14 together with the breech ring 22 and the bolt assembly 24. Soon after recoil begins, 'the rollers 46, carried by the projecting studs 58 of the bolt head 28, will engage cam unlocking surfaces 78 provided on an element 80 that is positioned rearwardly of breech ring 22 so as to induce relative rotation between the bolt head 2S and the remainder of the bolt assembly 24. This relative rotation serves to disengage the interrupted ring segments 42 and 44 whereby the bolt assembly 24 may continue to move into a recoil position.

It will be obvious to those skilled in the art that in this design the bolt head cams 52 are in contact with bolt head rollers 46 so that the initial locking rotation of bolt head 28 will force nose cams 52 rearwardly into seating engagement in slots 50 of bolt 26 before the bolt head 28 reaches its extreme locked position and while the bolt 26 is still moving forward. The rearwardly moving bolt head cams acting first through the springs 72, and then by direct contact with the bolt 26, will to a large extent counteract the forward energy of the bolt 26. The remaining energy of the bolt will carry the bolt cams 52 back into contact with the rolls 46. Continuing movement will complete the rotation of the bolt head 24, during which time the reaction from the rollers 46 will force the cams 52 outward into sliding engagement with the side walls of the receiver, and the friction resulting from this engagement will further dissipate the energy still remaining in the bolt.

In previous constructions which did not incorporate means for thus dissipating the bolt energy, there has been a tendency for the bolt to rebound from battery position with sutiicient energy to cause the unlocking cam to rotate the bolt head 28 at least partially out of locked position during the ignition period, and when this occurs the gas pressure will exert its force against the partially or completely unlocked bolt with serious results. By separating the cams from the bolt and providing an intermediate lost motion, the total kinetic energy of the bolt assembly available for useful work is not lessened, and after the useful work has been accomplished, energy which would otherwise cause dangerous rebound of the bolt is rendered ineffective by utilizing one portion of this energy to cancel out another portion thereof.

At the instant of the heaviest pressure between the cams 52 and rollers 46, there exists a lateral component force of this pressure tending to spread the cams apart. This aforementioned action that has been experienced in prior art sets up a detrimental condition that has been the cause of splitting of the bolts when the cam portion was an integral part thereof as used in present day guns.

4- In the instant disclosure this spreading component force acts to momentorily force the outward side faces of the cams 52 against the inside wall of the receiver resulting in a friction-damping action. Also the splitting force on the bolt is entirely eliminated.

From the foregoing description, it is thus seen that there is here provided an improved bolt mechanism that does employ cam portons that are replaceable and are cheap to manufacture. Further, the cam portions 54 are subjected to the entire amount of wear resulting from battering when contacting the rollers 46, therefore, when these component parts become greatly worn, they can be replaced without discarding the bolt 26.

l claim:

l. In a firearm having a receiver and a breech ring therein, a bolt assembly slidably mounted in the receiver for longitudinal movement between battery and recoil positions and comprising a bolt body, a bolt head rotatably carried by said bolt body and slidably disposed relative thereto, a roller projecting outwardly from said bolt head on either side thereof, a pair of inertia members slidably mounted in said bolt body adjacent the forward end thereof for relative limited longitudinal movement in either direction, spring means for normally urging said inertia members to the extreme forward position in said bolt body, and camming portions at the forward ends of said inertia members for rotating said bolt head into locked battery position, said inertia members being adapted for rearward movement upon impact between said bolt head rollers and the breech ring to reduce the counter-recoiling energy of said bolt body and being also adapted for forward inertia movement upon impact between said bolt body and said bolt head to counteract the tendency for said bolt body to bounce out of battery position.

2. in a firearm having a receiver and a breech ring therein, a bolt assembly slidably mounted in the receiver for longitudinal movement between battery and recoil positions and comprising a bolt body, a bolt head rotatably carried by said bolt body and slidably disposed relative thereto, an oppositely disposed pair of inertia members slidably mounted in said bolt body adjacent the forward and thereof for relative limited longitudinal reciprocation, spring means normally urging said inertia members to the extreme forward position in said bolt body, an oppositely disposed pair of rollers projecting outwardly from said bolt head, and camming portions at the forward ends of said inertia members for cooperating with said rollers to rotate said bolt head into locked battery position during movement of said bolt body into battery position, said inertia members being adapted for rearward movement upon impact between said bolt head rollers and the breech ring to reduce the counter-recoiling energy of said bolt body and being also adapted for forward inertia movement upon impact between said bolt body and said bolt head to counteract the tendency for said bolt body to bounce out of battery position.

3. In a firearm having a receiver and a breech ring therein, a bolt assembly slidably mounted in the receiver for longitudinal movement between battery and recoil positions and comprising a bolt body, a bolt head rotatably carried by said bolt body and slidably disposed relative thereto, an oppositely disposed pair of inertia members slidably mounted in said bolt body adjacent the forward end thereof for relative limited longitudinal movement in either direction, spring means for normally urging said inertia members to the extreme forward position in said bolt body, an oppositely disposed pair of rollers projecting outwardly from said bolt head, cam means in the breech ring for initiating locking rotation of said bolt head, and camming portions at the forward ends of said inertia members for cooperating with said rollers to complete the locking rotation of said bolt head during movement of said bolt body into battery position, said camming portions on said inertia members being helically contoured to provide a lateral force during the camming pressure on said bolt head rollers for moving said inertia members into frictional contact ith the receiver walls to reduce the countenrecoiling energy of said bolt body, said inertia members being adapted for rearward movement upon impact between said bolt 1iead rollers and said breech ring cam means to reduce the counter-recoiling energy of said bolt body and being also adapted for forward inertia movement upon impact between said bolt body and said bolt head to counteract the tendency for said bolt body to bounce out of battery position.

4. In a firearm having a receiver and a breech ring therein, a bolt assembly slidably mounted in the receiver for longitudinal movement between battery and recoil positions and comprising a bolt body having a pair of oppositely disposed slots opening forwardly in said body and a transverse recess through said body to provide communication between said slots, a bolt head having a rearwardly projecting shank slidably and rotatably mounted in said bolt body, an oppositely disposed pair of rollers projecting outwardly from said bolt head and forwardly of said shank, cam means in the breech ring operative on said bolt head rollers to initiate locking rotation of said bolt head, an L-shaped inertia member slidably mounted in each of said bolt head slots and extending into said transverse recess for limited longitudinal movement in either direction, spring means operative between the rear wall of said transverse recess and the rear surface of said inertia members to normally position said inertia members in the forwardmost position relative to said bolt body, said inertia members including camming portions projecting forwardly of said bolt body for cooperating with said rollers to complete the locking rotation of said bolt head during movement of said bolt body into battery position, said inertia members being adapted to seat in said bolt head slots in response to the rotation imparted to said bolt head rollers by said breech ring cam means and thereby reduce the counter-recoiling energy of said bolt body and being also adapted to move forwardly through inertia upon impact between said bolt body and said locked bolt head to counteract the tendency for said bolt body to bounce out of battery position.

5. In a rearm having a receiver and a breech ring therein, a bolt assembly slidably mounted in the receiver for longitudinal movement between battery and recoil positions and comprising a bolt body having a pair of oppositely disposed slots opening forwardly in said body and a transverse recess through said body to provide communication between said slots, a bolt head having a rearwardly projecting integral shank portion slidably and rotatably mounted in said bolt body, an oppositely disposed pair of rollers projecting transversely from said bolt head forwardly of said shank portion, cam means in the breech ring operative on said bolt head rollers to initiate locking rotation of said bolt head, an L-shaped inertia member slidably mounted in each of said bolt head slots and extending into said transverse recess into bearing relation with said bolt head shank portion, pin means for loosely retaining said inertia members in said bolt body, spring means normally urging said inertia members into the forwardmost position relative to said bolt body, said inertia members including camming portions projecting forwardly of said bolt body for cooperating with said rollers to complete the locking rotation of said bolt head during movement of said bolt body into battery position, said camming portions having angularly disposed helically contoured faces for imparting a lateral component of force for spreading said inertia members apart into frictional contact with the receiver walls during the camming pressure thereof on said bolt head rollers to reduce the counter-recoiling energy of said bolt body, said inertia members being adapted to seat rearwardly in said bolt body slots and recess as a result of the rotation imparted to said bolt head rollers by said breech ring cam means for reducing the counter-recoiling energy of said bolt body and being also adapted to seat forwardly in said bolt body slots and recess as a result of the impact between said bolt body and said locked bolt head for counteracting the rebound energy of said bolt body.

6. ln a firearm having a receiver, a rotatable bolt head longitudinally slidable therein for movement between a battery and a recoil position, roller means projecting transversely from the rear end of the bolt head, cam means in the receiver operative on the roller means to impart rotation to the bolt head into and out of locked battery position, and a longitudinally slidable bolt body engageable with the bolt head for limited reciprocal movement relative thereto, the improvement of an inertia member slidably mounted on either side of the bolt body to project forwardly from the front end thereof, means for limiting slidable movement of the inertia members in either direction, spring means normally biasing each of said inertia members forwardly into contact with the bolt head roller means during counter-recoil of the bolt head and bolt body, and an angularly disposed helical cam surface on the forward end of each of said inertia members engageable with the bolt head roller means for continuing the locking rotation of the bolt head during movement of the bolt body into battery, said helical cam surfaces on said inertia members being contoured to provide a lateral component of force during the camming pressure thereof on the bolt head roller means whereby said inertia members are transversely forced apart into frictional contact with the sidewalls of the receiver and thereby reduce the counter-recoiling energy of the bolt body.

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